1. Field of the Invention
The present invention relates to a radio selective calling receiver and, more particularly, to a radio selective calling receiver having a multiarea function and a reception restoring method therefor.
2. Description of the Prior Art
Currently, the number of radio selective calling receiver subscribers is steadily increasing. Along with popularization of such radio selective calling receivers, they are made compact and have high-level functions. Additionally, a variety of services are provided.
One of functions of a radio selective calling receiver which have recently received a great deal of attention is a so-called multiarea function. The user who is carrying the radio selective calling receiver sometimes moves among a plurality of areas. If the radio selective calling receiver has the multiarea function, the reception channel is automatically switched by this function, so the user can be called in any area.
Conventionally, the multiarea function of this type collates synchronization of a received signal at the set channel. When mismatching is detected in this synchronization signal collation, the number of times of mismatching is counted and accumulated. When the number of times of accumulation has reached a predetermined value, the reception channel is switched.
Channel switching upon an area change will be described below with reference to the block diagram of a conventional radio selective calling receiver shown in FIG. 1 and timing charts shown in FIGS. 2A and 2B. A base station (not shown) in each service area transmits a plurality of frames for every cycle having a predetermined time length. Each frame includes a synchronization signal and a selective calling signal subsequent to the synchronization signal.
To receive a specific frame for the radio selective calling receiver from the plurality of frames sent from the base station (not shown), the received data is sent to a synchronization signal collation unit 3 in a control unit 2 (arrow a).
The synchronization signal collation unit 3 supplies timing information of the data to a radio unit power timing generator 4 in synchronism with the data which has been transmitted from the base station and received by a radio unit 1 (arrow b).
The radio unit power timing generator 4 supplies a control signal for instructing ON/OFF control of the power supply for the radio unit 1 to a radio unit power control unit 5 such that only the specific frame for the radio selective calling receiver is received (arrow c).
The radio unit power control unit 5 ON/OFF-controls the power supply for the radio unit 1 in accordance with this control signal (arrow d). Under this control, the radio unit 1 performs an intermittent operation (battery saving) for every cycle in principle.
When synchronization with the data from the base station is detected by the synchronization signal collation unit 3, a selective calling signal collation unit 6 collates whether the selective calling signal next to the synchronization signal included in the specific frame for the radio selective calling receiver matches the calling signal of the radio selective calling receiver (arrow e). If the two signals match, a notification unit 7 performs notification of calling and displays the message (arrow f).
The reception channel of the radio unit 1 is set by a radio unit reception channel setting unit 8 using, e.g., a PLL control VCO (arrow g). For the first channel setting after power ON, the radio unit reception channel setting unit 8 is controlled by a reception channel control unit 9 such that, of a plurality of reception channels which have been registered in advance, a channel (first channel) with the highest priority is set (arrow h).
If no synchronization signal can be received by the synchronization signal collation unit 3 in the initial state (first channel) (arrow i), the reception channel is switched by the reception channel control unit 9 and the radio unit reception channel setting unit 8 (arrow h) to select a channel where the synchronization signal can be received, and a synchronization state is set to perform intermittent reception using this selected channel.
After reception of the synchronization signal and establishment of the synchronization state, if the synchronization signal of the specific frame for a certain cycle is not received by the synchronization signal collation unit 3, a signal is output to a synchronization signal consecutive nonreception counter 10 (arrows i and i'). When the number of times of consecutive nonreception of the synchronization signal of the specific frame has reached a predetermined value (arrows j and k), an out-of-area state is determined. The radio unit power timing generator 4 and the reception channel control unit 9 receive the specific frame using a channel except the current channel.
As described above, in the conventional radio selective calling receiver, when the number of times of consecutive nonreception of the synchronization signal has reached a predetermined value, the reception channel is sequentially switched on the basis of a certain algorithm. This channel switching is repeated until the synchronization signal can be received.
Each radio selective calling receiver in the service area intermittently receives a specific frame (frame 1 in FIGS. 2A and 2B) assigned to the receiver using a specific frame (CH1 in FIGS. 2A and 2B) as a reception channel. At the same time, battery saving control is performed to turn off the power supply for the radio unit in the nonreception period of intermittent reception. This state is called a synchronization state (FIG. 2A).
If the user of the radio selective calling receiver moves from the current area to another area, reception cannot be continued using the current reception channel, and the reception channel must be switched. For this purpose, the following control is performed.
Every time the radio calling receiver intermittently receives the specific frame, it is determined whether the synchronization signal of the frame has been normally received. If the synchronization signal could not be normally received, the number of times of consecutive nonreception (to be referred to as a consecutive nonreception count hereinafter) is counted.
When the consecutive nonreception count has reached a predetermined value, it is determined that the user is out of the area. An operation for selecting an appropriate channel corresponding to the new area is started. After channel selection, intermittent reception of the specific frame is restarted using the new reception channel (FIG. 2B).
In this case, since the channel to be selected is unknown, the reception (enable/disable state is determined while sequentially switching a plurality of candidate channels. By repeating this processing, an appropriate channel is selected.
The above-described radio selective calling receiver has the following problems.
(1) In the conventional radio selective calling receiver, the reception channel is not switched until the user reaches the boundary of areas and cannot be called. For this reason, before reception is enabled again, not only a time for detecting synchronization signal nonreception the predetermined number of times but also a time for a scanning operation for sequentially switching reception channels in number corresponding to the number of areas where reception by the receiver is enabled is required, so reception is disabled for a long time.
(2) The conventional radio selective calling receiver has large battery consumption. The reason for this is as follows. If the reception channel scanning interval in an area change is made short, resynchronization can be quickly established. However, when the radio wave of the system cannot be received, the out-of-area state, i.e., a state wherein the battery saving effect becomes small continues for a long time, and the battery is consumed.